1. Field of the Invention
The present invention relates in general to a high definition video cassette recorder (referred to hereinafter as VCR) connected to a high definition television receiver, and more particularly to a signal characteristic variation apparatus for the high definition VCR in which a characteristic of a video signal transmitted is varied according to characteristics of a tape and a channel for recording and playback of the video signal.
2. Description of the Prior Art
Referring to FIG. 1, there is shown a block diagram of a conventional high definition VCR connected to a high definition television receiver. In this drawing, the high definition VCR is designated by the reference numeral 20 and the high definition television receiver is designated by the reference numeral 10. The high definition television receiver 10 is adapted to receive a compressed high definition video signal transmitted from a broadcasting station and display the received video signal through a monitor (not shown) thereof. The high definition VCR 20 is adapted to record the high definition video signal received by the high definition television receiver 10 on a tape, play back the high definition video signal recorded on the tape and display the played back video signal through the monitor of the high definition television receiver 10.
The high definition television receiver 10 comprises a tuner 11 for detecting the compressed high definition video signal Vi from the broadcasting station, received through an antenna (not shown), a demodulator 12 for demodulating the detected video signal from the tuner 11 into a state before its modulation, a decoder 13 for receiving the demodulated video signal from the demodulator 12 through a switch SW1 when the high definition television receiver 10 is selected by the user and decoding the received video signal to expand it into a state before its compression, and a digital/analog (D/A) converter 14 for converting the decoded video signal from the decoder 13 into an analog video signal.
The high definition VCR 20 comprises an error correction coder 21 for receiving the demodulated video signal from the demodulator 12 through the switch SW1 when a recording mode of the high definition VCR 20 is selected by the user and adding an error correction code to the received video signal, a formatter 22 for formatting an output signal from the error correction coder 21 in a recording format on the tape, a channel modulator 23 for modulating an output signal from the formatter 22 suitably to a channel characteristic, a recording amplifier 24 for amplifying an output signal from the channel modulator 23 by a predetermined level, and a head HD1 for recording an output signal from the recording amplifier 24 on the tape.
Also, the high definition VCR 20 comprises a head HD2 for playing back a data stream of the video signal recorded on the tape when a playback mode of the high definition VCR 20 is selected by the user, a playback amplification/equalization circuit 25 for amplifying the data stream played back by the head HD2 by a predetermined level and compensating for a distortion of the amplified data stream, a channel demodulator 26 for demodulating an output signal from the playback amplification/equalization circuit 25 suitably to the channel characteristic, and a deformatter/error correction decoder circuit 27 for deformatting an output signal from the channel demodulator 26 into the original state, correcting an error of the resultant video signal and outputting the error-corrected video signal to the decoder 13 through the switch SW1.
The operation of the conventional high definition VCR with the above-mentioned construction will hereinafter be described.
First, in the case where the high definition television receiver 10 is selected by the user, the video signal compressed and modulated in the broadcasting station is received by the antenna and then tuned by the tuner 11. The tuned video signal from the tuner 11 is demodulated into the state before its modulation by the demodulator 12. In the demodulator 12, there is extracted and corrected an error component inserted into the video signal in the transmission. The demodulated video signal from the demodulator 12 is applied to the decoder 13 through the switch SW1.
the decoder 13 decodes the received video signal to expand it into the state before its compression. The decoded video signal from the decoder 13 is converted into the analog video signal by the D/A converter 14 and then displayed through the monitor.
On the other hand, in the case where the recording mode of the high definition VCR 20 is selected by the user, the switch SW1 is switched to transfer the demodulated video signal from the demodulator 12 to the error correction coder 21. The error correction coder 21 adds the error correction code to the demodulated video signal from the demodulator 12 to remove an error component to be generated in the recording of the video signal on the tape. Then, the formatter 22 formats the output signal from the error correction coder 21 in the recording format on the tape.
The output signal from the formatter 22 is modulated by the channel modulator 23 suitably to the channel characteristic corresponding to the head, the tape or the recording amplifier, so that it can be recorded at a limited recording frequency. The output signal from the channel modulator 23 is amplified by the predetermined level by the recording amplifier 24 and then recorded on the tape by the head HD1.
In the case where the playback mode of the high definition VCR 20 is selected by the user, the data stream of the video signal recorded on the tape is played back by the head HD2 and then amplified by the predetermined level by the playback amplification/equalization circuit 25. Also, the playback amplification/equalization circuit 25 compensates for the distortion of the amplified data stream. Then, the output signal from the playback amplification/equalization circuit 25 is demodulated by the channel demodulator 26 into the state before the modulation by the channel modulator 23.
The output signal from the channel demodulator 26 is deformatted into the original state by the deformatter/error correction decoder circuit 27. Also, the deformatter/error correction decoder circuit 27 corrects an error component of the resultant video signal generated in the recording and playback.
Then, the error-corrected video signal from the deformatter/error correction decoder circuit 27 is applied to the decoder 13 in the high definition television receiver 10 through the switch SW1. The decoder 13 decodes the received video signal to expand it into the state before its compression. The decoded video signal from the decoder 13 is converted into the analog video signal by the D/A converter 14 and then displayed through the monitor of the high definition television receiver 10.
Noticeably, an analog video signal of an NTSC or PAL system can be recorded at a frequency band of 5 MHz on a VCR tape of a VHS system. Also, in the case of a S-VHS system, the analog video signal can be recorded at a frequency band of 7 MHz. On the other hand, a digital video signal receivable by the high definition television receiver has an information amount much (at least 5 times) more than that of the analog video signal. For this reason, the digital video signal must be recorded at a density much higher than that of the analog video signal.
Therefore, the future-oriented high definition VCR can record the high definition video signal at a very high recording speed on high quality tapes of MP and ME systems as well as the SVHS system, differently from the existing analog VCR. Namely, the high definition video signal can be recorded at a frequency band of 15 MHz by the high definition VCR. By the way, in the high definition VCR, a channel characteristic or a recording/playback characteristic of the digital video signal is determined according to a characteristic of the tape as a recording medium. In this connection, the digital video signal may recorded and played back properly when the tape has a small capacity. The improper recording and playback of the digital video signal results in a degradation in a picture quality.